With the development of coding and information compression technologies and digital networks, people have developed video display systems, which may transport information such as motion images, voice, and application data in real time between two or more points.
One basic function of a video display system is to collect and display video images. During the process of displaying a video, a device at a receiving end receives compressed video bit streams, decodes the compressed video bit streams to obtain a video image, and then outputs the video image to a display device for display. When the video image is displayed on the display device, a foreground picture in the video images, for example, a face area, may be zoomed in or out. The display device is usually installed by a user, so the sizes and resolutions of display devices at different conference sites may vary and foreground pictures may produce different zooming effects. For example, when the resolutions are the same, a foreground picture of the genuine size of a human appears the genuine size of a human on a 52-inch display device, providing genuine experience. If the foreground picture is presented on a 62-inch display device, the foreground picture may appear obviously zoomed in. If the video image is presented on a 42-inch display device, the foreground picture may appear obviously zoomed out.
To sum up, in an existing video display system, the foreground picture in a video image may be zoomed in or out to different degrees when being displayed on display devices with different sizes and resolutions, making it hard to present the image in a constant size. Therefore, a certain degree of distortion occurs.